1. Field of Invention
The invention relates to a mixed oxide catalytic system containing MoVLaNbPdX (where X=Al, Ga, Ge, and/or Si) for low temperature, low pressure selective oxidation of ethane or ethane/ethylene to acetic acid. The invention also relates to methods of using the same including a single stage catalytic process featuring high space time yields of acetic acid.
2. Description of the Related Art
Several publications are referenced in this application. The references describe the state of the art to which this invention pertains and are hereby incorporated by reference.
The use of molybdenum and vanadium containing catalyst systems for low temperature oxydehydrogenation of ethane to ethylene was reported by E. M. Thorsteinson et al. "The Oxidative Dehydrogenation of Ethane over Catalyst Containing Mixed Oxide of Molybdenum and Vanadium", Journal of Catalysis, Volume 52, pp. 116-132 (1978). This paper relates to mixed oxide catalysts containing molybdenum and vanadium together with another transition metal oxide, such as Ti, Cr, Mn, Fe, Co, Ni, Nb, Ta, or Ce. The catalysts are active at temperatures as low as 200.degree. C. for the oxydehydrogenation of ethane to ethylene. Some acetic acid is produced as a by-product.
U.S. Pat. Nos. 4,250,346; 4,524,236; 4,568,790; 4,596,787; and 4,899,003 relate to the low temperature oxydehydrogenation of ethane to ethylene. The first of these references discloses the use of catalysts of the formula Mo.sub.h V.sub.i Nb.sub.j A.sub.k in which A is Ce, K, P, Ni and/or U, h is 16, i is 1 to 8, j is 0.2 to 10, and k is 0.1 to 5.
U.S. Pat. No. 4,454,236 is directed to the use of a calcined catalyst of the formula Mo.sub.a V.sub.b Nb.sub.c Sb.sub.d X.sub.e.
The above cited patents make reference to other patents concerned with the production of ethylene from ethane by the oxydehydrogenation process and all make reference to the formation of acetic acid as a by-product.
U.S. Pat. Nos. 4,339,355 and 4,148,757 relate to an oxide catalyst containing Mo, Nb, V and a fourth metal from Co, Cr, Fe, In, Mn or Y for the oxidation/ammoxidation of unsaturated aliphatic aldehyde to the corresponding saturated aliphatic carboxylic acids.
European Patent Publication No. 0 294 845 relates to a process for the higher selective production of acetic acid by the oxidation of ethane with oxygen in contact with a mixture of catalysts consisting of (A) a catalyst for oxydehydrogenation of ethane to ethylene and (B) a catalyst for hydration/oxidation of ethylene. The ethane oxydehydrogenation catalyst is represented by the formula Mo.sub.x V.sub.y Z.sub.z, wherein Z can be nothing or Nb, Sb, Ta or W.
European Patent Publication No. 0 480 594 is directed to the use of an oxide catalyst composition comprising tungsten, vanadium, rhenium and at least one of the alkaline metals for the production of ethylene and acetic acid by oxidation of ethane with a molecular oxygen containing gas.
The replacement of tungsten in whole or part by molybdenum carried out in European Patent Publication No. 0 407 091 results in an increase in selectivity to acetic acid at the expense of the selectivity to ethylene.
European Patent Publication No. 0 518 548 relates to a process for the production of acetic acid by ethane oxidation in contact with a solid catalyst having the empirical formula VP.sub.a M.sub.b O.sub.x, where M is one or more optional elements selected from Co, Cu, Re, Nb, W and many other elements, excluding molybdenum, a is 0.5 to 3 and b is 0 to 0.1.
European Patent Publication No. 0 627 401 relates to the use of a V.sub.a Ti.sub.b O.sub.x catalyst for the oxidation of ethane to acetic acid. The catalyst composition may comprise additional components selected from a large list of possible elements. The reference does not disclose any examples of catalysts comprising those elements in combination with vanadium, titanium and oxygen.
Furthermore, recently reported catalysts containing molybdenum, niobium and vanadium with other additional components or promoters are reported for similar ethane oxidation applications (Copending application Ser. Nos. 08/293,075; 08/997,913 and 09/107,115).
Thus, none of the prior art discloses or suggests the advantages of the catalytic system disclosed in present invention for the selective production of carboxylic acids such as acetic acid from ethane or mixtures of ethane/ethylene.
It would be desirable to provide a catalyst for use in an improved method of making acetic acid from ethane.